JPH0446895B2 - - Google Patents

Abstract

1. A process of producing aluminum fluoride from aluminum hydroxide or alumina hydrate and hydrogen fluoride in a circulating fluidized bed system including a fluidized bed reactor, a cyclone separator and a recycling line, characterized in that partly reacted aluminum hydroxide circulated in a cooling cycle is added to fresh aluminum hydroxide or alumina hydrate in a first stage, in which the aluminum hydroxide is contacted with the hydrogen fluoride-containing exhaust gases from the circulating fluidized bed system so as to form a gas-solids suspension at a temperature of 150 to 250 degrees C, whereafter the solids are collected from the gas stream, at least part of the collected solids are passed through a cooler, cooled solids are re-contacted with fresh aluminum hydroxide or alumina hydrate, and a partial stream of the collected solids is supplied to the circulating fluidized bed system and is reacted therein at a temperature of at least 450 degrees C with hydrogen fluoride supplied in the form of a gas in a concentration up to 25 vol. %.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses a circulating fluidized bed consisting of a fluidized bed reactor, a return cyclone, and a return pipe.
The present invention relates to a method for producing aluminum fluoride from aluminum hydroxide or aluminum oxide hydrate and hydrogen fluoride.

[Conventional technology]

Regarding the production of aluminum fluoride, there is a method in which a fluorine-containing substance is reacted with a mineral acid and then crystallized (West German Publication No. 1062681), a method in which a fluorine compound and aluminum chloride are reacted in two steps (Austrian patent) No. 130199, West German Patent No.
837690, US Patent No. 1881430), a method of reacting alumina or alumina hydrate with an aqueous hydrofluoric acid solution (West German Patent No. 1220839, West German Publication No. 1592099, No. 1592100, No. 1592195, US Patent No. 3492086) and method of decomposing aluminum alcoholate with acid (West German Publication No.
1294358), production methods using aluminum oxide hydrate or aluminum hydroxide and hydrogen fluoride are particularly important. In this case, the reaction can take place in the aqueous phase, followed by crystallization and, if necessary, also dehydration (DE 492 412). However, it is also possible to carry out the reaction at elevated temperatures so that water-free aluminum fluoride is obtained as the process product (UK Patent No. 328,688). In this case, in particular, fluidized bed processes are used, in which alumina or aluminum hydroxide is reacted with hydrogen fluoride gas at high temperatures (German patent no. 815343, no. 1092889, British patent no.
No. 656374, French Patent No. 1011544, No. 1221299,
No. 1517952, U.S. Patent No. 3057680). West German Publication No. 1908585, French Publication No. 2002335 and Canadian Patent No. 537403 disclose that aluminum oxide trihydrate and partially dehydrated aluminum oxide trihydrate are prepared by hydrogen fluoride-containing gas. A method for producing aluminum fluoride in steps is described.

The process described above, which involves crystallization and drying of aluminum fluoride, is of course multi-stage and therefore expensive in equipment. Additionally, there are significant drainage issues or the need to circulate large amounts of solvent. Fluidized bed processes commonly require relatively high concentrations of hydrogen fluoride gas.

Another process for producing aluminum fluoride is carried out using a circulating fluidized bed. In this case, liquid hydrogen fluoride is directly supplied above the rostrum of the fluidized bed but below the solids return section (German Patent No. 2106306). This process is particularly advantageous because the hydrofluoric acid passes virtually instantaneously through the critical temperature range of 60 to 250°C with respect to corrosion and immediately reaches the fluidized bed temperature; This assumes the existence of hydrogen fluoride.

Recently, a method of producing aluminum fluoride using a gas having a relatively low concentration of hydrogen fluoride has been gaining importance. This type of gas is obtained from hydrothermal decomposition processes of solid residues (e.g. furnace effluents) in the aluminum industry and, depending on the mode of operation in the concentration process and subsequent gas treatment, only 8 to 12 volumes %
Or it only contains 20-25% by volume of hydrogen fluoride. Moreover, the water vapor content of this gas is extremely high, reaching up to 70% by volume.

[Problem that the invention seeks to solve]

Due to the above-mentioned circumstances, the following problems occur during the production of aluminum fluoride.

That is, as the reaction temperature of the aluminum fluoride reactor increases and the water vapor content in the gas increases, the equilibrium partial pressure of hydrogen fluoride in the exhaust gas increases.

This means that the recovery rate (conversion rate) of hydrogen fluoride decreases rapidly as the exhaust gas temperature rises and the water vapor content increases. Due to the still existing goal of obtaining as high a concentration of aluminum fluoride as possible (eg, at least 90% by weight AlF ₃ ), lowering the reaction temperature does not yield the desired results. The reason is that although the equilibrium conditions are improved to achieve a high recovery of hydrogen fluoride, the reaction rate (Kinetik) of the process is significantly reduced. It is not industrially feasible to compensate for the significant reduction in reaction rate by increasing the residence time of the solids in the reactor, given the volumes that would then be required.

[Means for solving problems]

In view of the above problems, the present invention aims to achieve the highest possible hydrogen fluoride recovery (conversion rate) that can be carried out in an industrially appropriate scale reactor using a gas with a low hydrogen fluoride content. At the same time, it is an object of the present invention to provide a method for producing aluminum fluoride that can produce a highly concentrated product.

This purpose is achieved in a process of the type mentioned at the outset, according to the invention, in which in the first stage freshly charged water is passed through a cooling cycle and with the addition of already partially reacted aluminum hydroxide. Contacting aluminum oxide or aluminum oxide hydrate with hydrogen fluoride-containing off-gas in a circulating fluidized bed to form a gas/solids suspension with a mixing temperature of 150-250°C to separate solids from the gas stream. passing at least a portion of the separated solids through a cooler, further contacting the cooled solids with freshly supplied aluminum hydroxide or aluminum oxide hydrate, and passing a partial stream of the separated solids through a circulating flow system. This is achieved by feeding the hydrogen fluoride into a bed and reacting in this bed with hydrogen fluoride fed in gaseous form at a concentration of up to 25% by volume at a temperature of at least 450°C.

In the production of aluminum fluoride, aluminum oxide is first partially reacted with the high-temperature hydrogen fluoride-containing exhaust gas of the calciner in the exhaust gas pipe of the calciner, before reacting with 70-80% hydrofluoric acid. It is known to carry out the reaction and to appropriately design the exhaust gas pipes so that the exhaust gas and the aluminum oxide are in close contact (see German Publication No. 1956943).
issue). However, there is no simultaneous addition and mixing of the aluminum hydroxide which has been passed through the cooling cycle and has already partially reacted. In this known method, this mixing operation is not necessary. Because in this case the hydrofluoric acid used is highly concentrated, the ratio of exhaust gas stream to aluminum oxide is essentially favorable in terms of heat balance.

Within the scope of the process according to the invention, it is possible to use filtered, moist or predried aluminum hydroxide or aluminum oxide hydrate as solid material.

The amount of aluminum hydroxide added through the cooling cycle essentially depends on the temperature of the cooled hydroxide and the temperature of the gas/solids suspension forming gas. It is necessary to achieve a mixing temperature of 150-250°C, thereby significantly increasing the recovery (conversion) of hydrogen fluoride in the first stage of the process.

In a configuration suitable for the purposes of the invention, the entire amount of solids separated from the gas/solids suspension is passed through a cooler. This ensures, inter alia, that a sufficient amount of solids is obtained to cool the exhaust gas to the desired temperature.

According to another embodiment of the invention, hydrogen fluoride supplied in gaseous form is reacted in a circulating fluidized bed at a temperature in the range of 500 DEG to 600 DEG C. This temperature range allows, on the one hand, to carry out the reaction sufficiently fast and, on the other hand, to obtain a suitable exhaust gas temperature without unnecessary cooling costs in the cooling cycle.

In a preferred embodiment of the invention, the portion of the solids that is fed to the circulating fluidized bed is fed via a separator by the exhaust gas stream of the circulating fluidized bed. In this way, the exhaust gas stream is considerably cooled and, furthermore, the reaction section is increased.

In a variant of the method according to the invention, the exhaust gas stream leaving the return cyclone of the circulating fluidized bed, besides being cooled with aluminum hydroxide, is furthermore provided with a charge of cold gas, for example air at ambient temperature. cooled down. As a result, the amount of aluminum hydroxide sent to the cooling cycle can be reduced. This configuration allows, in particular, additional control over the temperature of the gas before the start of contact with fresh charge material, regardless of the material flow of the process.

All known devices suitable for this purpose can be used as coolers for the aluminum hydroxide separated from the gas/solids suspension. Particularly suitable are fluidized bed coolers with optionally several chambers through which aluminum hydroxide flows and water-cooled cooling surfaces connected to one another and accommodated in each chamber.

The circulating fluidized bed is constructed and operated in a conventional manner. In other words, the fluidized bed cooler may have a circular, square or rectangular cross section and may have a rostre- or bench-lily-shaped charging device for charging the fluidizing gas. The area of the reactor and the amount of gas are as follows: The average density of the suspension is 1 m ³ of the reactor capacity.
They are mutually balanced to be in the range of 50-400Kg per unit. In this case, in a circulating fluidized bed - unlike a conventional fluidized bed, which is characterized by an abrupt change in density between the fluidized bed and the gas stream above it - the entire fluidized bed reactor is filled with gas/solids. It must be taken into account that it is filled with suspension and that the density of the suspension decreases from bottom to top. (For information on how to operate a circulating fluidized bed,
“Fluidized Bed Processes for Chemical Industry, Refining Industry, Energy Conversion and Environmental Protection” by L. Reh et al.
Chem, Ing, Techn, 55 (1983) No. 2, P87-93
[Examples] The present invention will be described in detail below with reference to the drawings and examples. In addition, the amount shown in the unit m ² _N in the examples represents the volume of gas (m ³ ) under standard conditions (0° C., 1 atm).

A circulating fluidized bed consisting of a fluidized bed reactor 1, a return cyclone 2, and a return line 3 is supplied with hydrogen fluoride-containing gas from a line 4. This gas is
The temperature may be raised to the required temperature by indirect heating or by addition of combustion gas. The exhaust gas is discharged from the return cyclone 2 of the circulating fluidized bed,
In the bench-lily suspension heat exchanger 5 , it is mixed with the solids fed via line 7 from the fluidized bed cooler 6 . The gas/solids suspension produced then enters a cyclone separator 9 via line 8 where the solids are separated and passed through line 1.
0, fluidized bed reactor 1, return cyclone 2,
and a return line 3 to a circulating fluidized bed.

In another mode of operation for captive cooling of the gas discharged from the return cyclone 2, cold gas (for example air at ambient temperature) is introduced through line 24.

The exhaust gas from the cyclone separator 9 is transferred to another bench-lily suspension heat exchanger 11 with freshly charged aluminum hydroxide or aluminum oxide hydrate from a line 22 and from a fluidized bed cooler 6 for temperature control. It is mixed with further solids introduced via line 12 to form a new gas/solids suspension. This suspension enters the cyclone separator 14 via line 13, where the solids are separated and fed via line 15 to the fluidized bed cooler 6. The exhaust gas is finally purified in a fines remover 16 (fabric filter or electrostatic filter) and fed to a wet or dry washer (not shown) for removal of residual hydrogen fluoride.

The fluidized bed cooler 6 comprises interconnected cooling surfaces 1
It has two cooling chambers 17 and 18 that accommodate 9.
The fluidizing gas is supplied from the pipe line 20. The solids stream leaving the fluidized bed cooler is distributed to lines 7, 12 by bucket-wheel distribution gates 21.

The final product is removed from the circulating fluidized bed via line 23.

Example 1 From pipe 4 to fluidized bed reactor 1 of circulating fluidized bed
^6906m3 of gas at a temperature of 570℃ containing 10.1% by volume of HF
It was supplied at a rate of _N2 /h. The temperature of the circulating fluidized bed is
It was 530℃. The average density of the suspension is
The amount was 150 kg per ^m3 of reactor volume. The amount of solids circulated through the fluidized bed reactor 1, return cyclone 2 and return line 3 was 50 times the amount of solids present in the fluidized bed reactor 1.

The exhaust gas from the circulating fluidized bed is 530℃ and HF concentration is 7.5.
% by volume enters the bench lily suspension heat exchanger 5, where it is mixed with 100°C solids supplied from the fluidized bed cooler 6 via line 7 at a rate of 1797 kg/h. Ta. This cooled the gas to 453°C. The solids separated in the cyclone separator 9 were introduced through a pipe 10 into a fluidized bed reactor 1 of a circulating fluidized bed.

The exhaust gas with an HF content of 4.0% by volume exiting the cyclone separator 9 is transferred to a bench lily suspension heat exchanger 1.
1, fresh aluminum hydroxide or aluminum oxide hydrate (1030
kg/h; moisture 12.0%) and the solids (16,500 kg/h; 100° C.) introduced via line 12 by means of 1000 m ³ _N /h of turbulent air from the fluidized bed cooler 6. This cooled the exhaust gas to 220°C.
The exhaust gas passed through a cyclone separator 14 and a fine powder remover 16, and then led to a dry washer. The exhaust gas contains 0.15% by volume of HF, and the amount of exhaust gas produced is
It was ^8100m3N _/ h.

The solid matter at 220°C separated in the cyclone separator 14 and the fine powder remover 16 is cooled to 100°C in the fluidized bed cooler 6, and then transferred to the pipe line 7 and the pipe line 12 at a ratio of 1:9.2 as described above. It was distributed.

As a product, 937 kg/h of aluminum fluoride was taken out from the fluidized bed reactor 1 through line 23. Its purity was 91% (remaining Al ₂ O ₃ and loss on ignition).

Example 2 This example is an implementation of the method of the invention where supplementary air cooling is provided. The conditions regarding the gas supply and the operating mode of the circulating fluidized bed are the same as in Example 1.

The exhaust gas of the circulating fluidized bed was the same as in Example 1.
Bench lily suspension heat exchanger 5 at 530℃
In this heat exchanger, 100℃ was supplied from the fluidized bed cooler 6 through the pipe 7 at a rate of 1786Kg/h.
of solid matter. Furthermore, 40℃ from pipe 24
of air was supplied at a rate of 1052 m ³ _N /h. This cooled the gas to 420°C. The solids separated in the cyclone separator 9 were introduced through a pipe 10 into a fluidized bed reactor 1 of a circulating fluidized bed.

The exhaust gas with an HF content of 2.0% by volume exiting the cyclone separator 9 is transferred to a bench lily suspension heat exchanger 1.
1, fresh aluminum hydroxide or aluminum oxide hydrate (1030
kg/h; moisture 12.0%) and the solids (15900 kg/h; 100° C.) introduced via line 12 by means of 1000 m ³ _N /h of swirling air from the fluidized bed cooler 6. This cooled the exhaust gas to 220°C.
The exhaust gas passed through a cyclone separator 14 and a fine powder remover 16, and then led to a dry washer. The exhaust gas contains 0.13% by volume of HF, and the amount of exhaust gas produced is
It was ^9150m3N _/ h.

The solid matter at 220°C separated in the cyclone separator 14 and the fine powder remover 16 is cooled to 100°C in the fluidized bed cooler 6, and then transferred to the pipe line 7 and the pipe line 12 at a ratio of 1:8.9 as described above. It was distributed.

As a product, 937 kg/h of aluminum fluoride was taken out from the fluidized bed reactor 1 through line 23. Its purity was 91% (remaining Al ₂ O ₃ and loss on ignition).

The invention can be summarized as follows.

In a method for producing aluminum fluoride from aluminum hydroxide or aluminum oxide hydrate and hydrogen fluoride, in order to obtain a highly concentrated product and an exhaust gas with a low hydrogen fluoride content, in the first stage, it is sent to a cooling cycle. and with the addition of the already partially reacted aluminum hydroxide, the freshly charged aluminum hydroxide or aluminum oxide hydrate is brought into contact with the hydrogen fluoride-containing exhaust gas of a circulating fluidized bed, A gas/solids suspension is formed with a mixing temperature of .degree. Then,
Solids are separated from the gas stream, at least a portion of the separated solids is passed through a cooler, and the cooled solids are further contacted with freshly supplied aluminum hydroxide or aluminum oxide hydrate. The separated solid fraction is introduced into a circulating fluidized bed where it reacts at a temperature of at least 450°C, preferably between 500 and 600°C, with hydrogen at a concentration of up to 25% by volume, which is charged in gaseous form. let

In an advantageous configuration of the process, the entire amount of solids separated from the gas/solids suspension is passed through a cooler or the part of the solids that is fed to the circulating fluidized bed is added to the exhaust gas stream of the circulating fluidized bed. Therefore, it is fed through a separator.

[Brief explanation of drawings]

The accompanying drawings are a schematic flow diagram of the method of the invention. In addition, in the symbols used in the drawings, 1...
Fluidized bed reactor, 2... Return cyclone, 3...
Return pipe line, 5, 11... Bench lily type suspension heat exchanger, 6... Fluidized bed cooler, 9, 14
... Cyclone separator, 16 ... Fine powder remover, 2
1...Distribution gate.

Claims (1)

[Claims] 1. Producing aluminum fluoride from aluminum hydroxide or aluminum oxide hydrate and hydrogen fluoride using a circulating fluidized bed consisting of a fluidized bed reactor, a return cyclone, and a return pipe. In the process, in the first stage, a fresh charge of aluminum hydroxide or aluminum oxide hydrate is passed through a cooling cycle and with the addition of already partially reacted aluminum hydroxide, the body of a circulating fluidized bed is heated. contacting a hydrogen chloride-containing exhaust gas to form a gas/solids suspension at a mixed temperature of 150 to 250°C, separating solids from the gas stream, and passing at least a portion of the separated solids through a cooler; The cooled solids are further contacted with freshly supplied aluminum hydroxide or aluminum oxide hydrate, and a partial stream of the separated solids is fed to a circulating fluidized bed in which the gaseous gas is fed. A process characterized in that it is reacted with hydrogen fluoride at a concentration of up to 25% by volume at a temperature of at least 450°C. 2. Process according to claim 1, characterized in that the entire amount of solids separated from the gas/solids suspension is passed through a cooler. 3. The method according to claim 1 or 2, characterized in that the reaction in a circulating fluidized bed is carried out at a temperature of 500 to 600°C. 4. Claim 1, characterized in that a portion of the solids to be supplied to the circulating fluidized bed is supplied through a separator by the exhaust gas stream of the circulating fluidized bed.
3. The method according to paragraph 2, paragraph 3.